Background: Biofilm formation is a major virulence factor contributing to the chronicity of infections. To date few\r\nstudies have evaluated biofilm formation in infecting isolates of patients including both Gram-positive and\r\nGram-negative multidrug-resistant (MDR) species in the context of numerous types of infectious syndromes. Herein,\r\nwe investigated the biofilm forming capacity in a large collection of single patient infecting isolates and compared\r\nthe relationship between biofilm formation to various strain characteristics.\r\nMethods: The biofilm-forming capacity of 205 randomly sampled clinical isolates from patients, collected from\r\nvarious anatomical sites, admitted for treatment at Brooke Army Medical Center (BAMC) from 2004ââ?¬â??2011, including\r\nmethicillin-resistant/methicillin susceptible Staphylococcus aureus (MRSA/MSSA) (n=23), Acinetobacter baumannii\r\n(n=53), Pseudomonas aeruginosa (n=36), Klebsiella pneumoniae (n=54), and Escherichia coli (n=39), were evaluated for\r\nbiofilm formation using the high-throughput microtiter plate assay and scanning electron microscopy (SEM).\r\nRelationships between biofilm formation to clonal type, site of isolate collection, and MDR phenotype were\r\nevaluated. Furthermore, in patients with relapsing infections, serial strains were assessed for their ability to form\r\nbiofilms in vitro.\r\nResults: Of the 205 clinical isolates tested, 126 strains (61.4%) were observed to form biofilms in vitro at levels\r\ngreater than or equal to the Staphylococcus epidermidis, positive biofilm producing strain, with P. aeruginosa and S.\r\naureus having the greatest number of biofilm producing strains. Biofilm formation was significantly associated with\r\nspecific clonal types, the site of isolate collection, and strains positive for biofilm formation were more frequently\r\nobserved to be MDR. In patients with relapsing infections, the majority of serial isolates recovered from these\r\nindividuals were observed to be strong biofilm producers in vitro.\r\nConclusions: This study is the first to evaluate biofilm formation in a large collection of infecting clinical isolates\r\nrepresenting diverse types of infections. Our results demonstrate: (1) biofilm formation is a heterogeneous property\r\namongst clinical strains which is associated with certain clonal types, (2) biofilm forming strains are more frequently\r\nisolated from non-fluid tissues, in particular bone and soft tissues, (3) MDR pathogens are more often biofilm\r\nformers, and (4) strains from patients with persistent infections are positive for biofilm formation.
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